This invention relates to improvements in lift truck load handling attachments of the type whereby a load may be carried in a central position and extended transversely to the side of the truck when desired. More specifically, the attachment is of a type particularly adaptable for transporting elongate loads longitudinally through relatively narrow warehouse aisles, wherein the load handling forks may be extended sideways from the longitudinal center line of the truck to pick up or deposit the load.
In side loading or narrow-aisle attachments of the type known to the art and shown for example in Stanton, U.S. Pat. No. 3,599,818; Dixon, U.S. Pat. No. 3,390,798; and Ulinski, U.S. Pat. No. 2,709,017; a supporting boom is rigidly fixed to the lift truck carriage with a laterally rotatable fork assembly depending from its forward end. Because the boom is fixed to the carriage and therefore cannot swing laterally from side to side, each of the aforementioned devices must include a pantographic or similar type power linkage adjacent the fork assembly to extend the forks laterally. The requirement for such lateral extension devices and their respective motors makes the attachment relatively complicated and expensive and, what is more significant, adds considerable weight to the front of the boom assembly thereby detracting substantially from the load-lifting capability of the truck. The resultant reduction in truck stability limits both the weight and length of a given load which may safely be transported and elevated in a longitudinal position with respect to the truck.
Another general type of side loading attachment is illustrated in Ohntrup et al, U.S. Pat. No. 3,572,530 and Hansen, U.S. Pat. No. 3,672,526. These patents each feature a fork assembly carried by the outer end of a laterally swinging member mounted on the lift truck carriage, the lateral movement of such member providing at least a limited degree of transverse fork extension. However in neither case does the fork assembly depend from the swinging member in such a way that, with the forks situated transversely in the center of the truck, the load may be carried beneath the swinging member. With reference to the Ohntrup et al patent, this deficiency makes it impossible for the attachment to carry loads longitudinally in the center position without the added provision of a side shifting assembly and its related motor, which in turn add to the expense and weight of the attachment. In the case of Hansen, wherein the fork assembly and load are situated above the laterally swinging member, an auxiliary set of lifting cylinders must be provided at the front of the attachment in order to lift the load above the swinging member to thereby permit proper load positioning. This requirement likewise increases the weight and complexity of the attachment.
A third type of device is that depicted in Stevens, U.S. Pat. No. 3,272,365. This device, which is not an attachment but rather requires basic modification of the lift truck, utilizes a laterally swinging boom having so much weight forwardly of the center of gravity of the truck that an auxiliary caster at the base of the fork assembly is required to enable the truck to handle sufficient loads. Obviously the requirement for such an auxiliary caster limits severly the maneuverability of the truck and makes it quite difficult for the truck to negotiate ramps or other uneven surfaces.
Accordingly, a great need exists in the lift truck industry for a relatively inexpensive and uncomplicated load handling attachment having side loading and side extending capability for use in narrow aisle situations, such attachment having a minimum of heavy mechanical components and a minimum of weight at its forward end, thereby maximizing the load-carrying capability of the truck and enabling loads of substantial length and weight to be handled, particularly in a longitudinal position with respect to the truck.